All "Low Digits" are technically stolen. Low Digit accounts are obtained in one of the following ways: Brute Forced, E-Mail Recovered, or CD-Key Recovered.

All accounts sellers deem as securable are not actually securable, this is a lie told to advance the sale. The account creator can recover the account at any given time. You can buy 1,000 games and still lose the account to the original owner. They have no time limit either.

Just because you have the Half-Life CD-Key for an account does not mean you are deemed the owner. People obtain these keys for the accounts in many ways either by photoshopping a template and making a ticket or buying random keys on eBay and recovering the associated accounts. Valve is aware of this and if they have enough probable cause, they will reclaim the account or issue a community ban.

POPs don't matter, they just don't. For years people have been advertising that their accounts "Come with Proof of Purchases." This just does not matter. Even if they provide it, and "delete their proofs," they can just make a support ticket and reclaim the account within hours.

It is not a good idea to buy bulk pre-registered accounts. People sell these accounts with "5$ deposit paid" or whatever their label is. Not only can they simply recover these accounts, you put yourself at risk for being flagged for actions you did not commit. For example, let's say the person who sold you the accounts was a scammer and their main and alts got trade banned, your accounts become at risk for also being flagged. Same with buying and selling related community bans, etc.

The bottom line, there is no safe trading accounts. You are better off creating your own.

Any questions, feel free to ask. I have had the worst experience with these activities with Valve in the past and thought it would be good to pass what I learned off to the community.